Pollutant removal from municipal wastewater employing baffled subsurface flow and integrated surface flow-floating treatment wetlands

This article reports pollutant removal performances of baffled subsurface flow, and integrated surface flow-floating treatment wetland units, when arranged in series for the treatment of municipal wastewater in Bangladesh. The wetland units （of the hybrid system） included organic, inorganic media, and were planted with nineteen types of macrophytes. The wetland train was operated under hydraulic loading fluctuation and seasonal variation. The performance analyses （across the wetland units） illustrated simultaneous denitrification and organics removal rates in the first stage vertical flow wetland, due to organic carbon leaching from the employed organic media. Higher mean organics removal rates （656.0 g COD]（m2.day）） did not completely inhibit nitrification in the first stage vertical flow system; such pattern could be linked to effective utilization of the trapped oxygen, as the flow was directed throughout the media by the baffle walls. Second stage horizontal flow wetland showed enhanced biodegradable organics removal, which depleted organic carbon availability for denitrification. The final stage integrated wetland system allowed further nitrogen removal from wastewater, via nutrient uptake by plant roots （along with nitrification）, and generation of organic carbon （by the dead macrophytes） to support denitrification. The system achieved higher E. coli mortality through protozoa predation, E. coli oxidation, and destruction by UV radiation. In general, enhanced pollutant removal efflciencies as demonstrated by the structurally modified hybrid wetland system signify the necessity of such modification, when operated under adverse conditions such as： substantial input organics loading, hydraulic loading fluctuation, and seasonal variation.

Ammoniacal Nitrogen and Organics Removal Modelling in Vertical Flow Wetlands Treating Strong Wastewaters

This paper reports a comparative evaluation between 2 kinetic models for predicting nitrification and biodegradable organics(BOD5)removal rates in 5 vertical flow(VF)wetland systems,that received strong wastewaters(i.e.tannery,textile and municipal effluents).The models were formulated by combining first order and Monod kinetics,with continuous-stirred tank reactor(CSTR)flow approach.The performance of the 2 models had been evaluated with3 statistical parameters:coefficient of determination(R2),relative root mean square error(RRMSE),and model efficiency(ME).The statistical parameters indicated better performance of the Monod CSTR model(over first order CSTR approach),for correlating ammoniacal nitrogen(NH4+—N)and BOD5removal profiles across VF systems.Higher Monod coefficient values(from Monod CSTR model)coincided with greater input NH4+—N and BOD5loading,and experimentally measured removal rate(g/(m2·d))values.Such trends indicate that NH4+—N and BOD5removals in the VF systems were mainly achieved via biological routes.On the other hand,the rate constants(from the first order CSTR model)did not exhibit such correlations(of Monod coefficients),elucidating their inefficiencies in capturing overall removal mechanisms.The interference of organics removal on nitrification process(in VF wetlands)was identified through Monod coefficients.The deviation between NH4+—N and BOD5Monod coefficients imply incorporation of both coefficients,for calculating the area of a single VF bed.Overall,closer performance of the Monod CSTR model for predicting NH4+—N and BOD5removals indicate its potential application,as a design tool for VF systems.

A Comparative Study of Pollutant Removal Stability in Hybrid Wetland Columns

This study investigated the effects of two alternative substrates(wood mulch and zeolite) on the performance of three laboratory-scale hybrid wetland systems that had identical system components and configurations.Each system consisted of a vertical flow(VF) wetland column,followed by a horizontal flow(HF) column and a vertical flow column.The substrates employed were wood mulch,gravel and zeolite,and Phragmites australis were planted in each column.The systems received synthetic wastewater,with pollutant loadings in the range of 8.5-38.0 g/(m2·d) total nitrogen(TN) and 4.0-46.4 g/(m2·d) biological oxygen demand(BOD5).Wood mulch and zeolite substrates showed higher efficiencies in terms of removing nitrogenous compounds and biodegradable organics.The supply of organic carbon from the organic mulch substrates enhanced denitrification,while adsorption of influent ammoniacal nitrogen(NH4-N) in zeolite played a major role in the removal of nitrogenous species in the wetland columns.Overall,the average percentage removals of TN and BOD5 reached >66% and >96% respectively,indicating stable performances by the hybrid wetland systems under the experimental loading ranges.Mathematical models were developed,based on the combination of Monod kinetics and continuously-stirred tank reactor(CSTR) flow patterns to describe the degradation of nitrogenous compounds.Predictions by the models closely matched the experimental data,indicating the validity and potential application of Monod kinetics in the modelling and design of treatment wetlands.